A noise filter serves to improve a signal to noise ratio (SNR) by reducing noise inputted to a system from an image sensor.
However, a generally used noise filter performs smoothing of an entire image in order to remove the noise, and as a result, image quality becomes deteriorated.
For example, noise filters such as a mean filter, a medium filter, and a Gaussian filter, smooth an image of an object by assuming pixel values of the entire image include the same general noise without differentiating detail areas such as an edge or a boundary of the image and texture areas expressing a texture and a grain of the object. That is, the filters do not differentiate between areas of the image having details or textures with those areas having general information.
Therefore, as a pixel of an image becomes higher, resolution decreases and overall quality of the image deteriorates.